The pyrazolo[3,4,5-kl]acridine ring system is known, although not in fully aromatic form. The following reports are representative of the known literature for the pyrazolo[3,4,5-kl]acridine ring system: Tetrahedron Lett. 1970, 3091; J.C.S. Perkin I, 1973, 2697; Chem. Ber., 109, 1898 (1976).